This application is based on application No. JP2000-332792 filed in Japan, the contents of which is hereby incorporated by reference.
1. Field of the Invention
This invention relates to an improved driving apparatus, and more particularly relates to a driving apparatus using an improved electromechanical conversion element.
2. Description of the Related Art
There have hitherto been proposed various types of driving apparatuses using as the driving source electromechanical conversion elements formed of a piezoelectric, electrostrictive or magnetostrictive material.
For example, as shown in the simplified illustration of FIG. 1(a), a driving apparatus has been proposed in which a driving member S is fixed to one lengthwise end of a piezoelectric element M while the other lengthwise end is fixed to a fixing member B, such that a driven member A is frictionally engaged with the driving member S.
Using a driving apparatus of this type, as shown in FIG. 1(b) for example, when the piezoelectric element M slowly extends, the driving member S and driven member A move together due to the frictional force therebetween. In other words, in FIG. 1(d) in which the horizontal axis represents the time T and the vertical axis represents the displacement Y, the displacement L1 of the piezoelectric element M over time and the displacement K1 of the driven member A over time roughly match each other.
On the other hand, where the piezoelectric element M rapidly contracts as shown in FIG. 1(c), slipping occurs between the driving member S and the driven member A, resulting in movement of the driving member S only with the driven member A being stationary. In other words, in FIG. 1(d), in contrast with the displacement L2 of the piezoelectric element M over time, there is little change in the displacement K2 of the driven member A over time.
When this basic operation principle is repeatedly applied, the driven member A may be moved in a relative fashion in a desired direction along the driving member S.
A specific example of such a driving apparatus is shown in the perspective view of FIG. 2 illustrating the components thereof in a disassembled fashion.
Using the driving apparatus 5, basically, a driven member 8 and a driving member 6 are housed in one space 9a of a housing 9 while a piezoelectric element 7 is housed in another space 9b thereof. One lengthwise end of the piezoelectric element 7 is bonded to an end of the driving member 6, and the other lengthwise end of the piezoelectric element 7 is bonded to the housing 9. The driving member 6 passes through and is held inside pierced holes 9s and 9t formed in the housing 9. A driven member 8 has a slider 8d through which the driving member 6 passes, a friction member 8c that is pressurized by the driving member 6 in the slider, and a plate spring 8b that is fixed to the slider 8d at both ends thereof using screws 8a and the middle portion of which presses down the friction member 8c. 
Incidentally, the conventional driving apparatus described above has the following characteristics.
FIG. 3 shows the driving characteristic obtained when a driving voltage having rectangular waves with a 0.3 duty ratio is impressed to the piezoelectric element 7 of this driving apparatus 5. The vertical axis represents the moving speed of the driven member 8. The horizontal axis represents the driving frequency of the driving voltage which was standardized (rendered dimensionless) by dividing it by the resonance frequency of the piezoelectric element 7, and the graph shows the results of measurement taken in the range between 0.6 and 0.9. As shown in the graph, the driven member 8 generally tends to move faster as the driving frequency increases.
However, the characteristic curve fluctuates dramatically up and down, and large drops in moving speed are also seen, indicating substantial fluctuation in the driving characteristic. Substantial fluctuation in the driving characteristic as in this example leads to a reduction in the performance of the apparatus.
Therefore, in order to ensure efficient driving and a stable driving speed, the driving frequency must be strictly controlled so that driving frequencies that would cause a drop in speed can be avoided. In addition, if there are large variations in the driving characteristic among driving apparatuses 5 having the same construction, a special adjustment will be required, such as checking for and setting the optimal control parameters for each of the driving apparatuses 5.
The present invention was created in view of the above situation, and an object thereof is to provide an improved driving apparatus. More particularly, an object of the present invention is to provide a driving apparatus having improved performance through the prevention of fluctuations in the driving characteristic.
In order to attain these and other objects, the driving apparatus according to one aspect of the present invention includes an electromechanical conversion element, a driving member that is fixed to one lengthwise end of the electromechanical conversion element, a driven member that is engaged with the driving member using a prescribed frictional force, a platform that is fixed to the other lengthwise end of the electromechanical conversion element, a housing that holds the platform, and a driver that impresses to the electromechanical conversion element a driving voltage by which to move the driven member, wherein the platform is elastically held relative to the housing.
Based on the above construction, when a driving voltage having an appropriate waveform is impressed to the electromechanical conversion element, the electromechanical conversion element extends and contracts. The oscillation caused by such extension and contraction is transmitted to the driving member, such that the driven member, which is engaged with the driving member using a prescribed frictional force, moves relative to the electromechanical conversion element.
When this occurs, it may seem that both the driving member and the platform oscillate due to the extension and contraction of the electromechanical conversion element. However, because the platform is elastically held by the housing, the transmission of the oscillation is reduced or blocked between the platform and the housing. Consequently, the housing may be prevented from resonating based on the oscillation, which is caused by the extension and contraction of the electromechanical conversion element being transmitted from the platform to the housing. Furthermore, even if the housing resonates, the transmission of such oscillation from the housing to the platform may be reduced or blocked. In other words, the drops in speed at specific frequencies that may have been caused by the characteristic oscillation of the housing, which was present in the prior art, may be prevented, and as a result, fluctuations in the driving characteristic may be prevented and the performance of the apparatus may be improved.
Specifically, the present invention may be realized using various forms as described below.
In the driving apparatus according to another aspect of the invention, the platform is bonded to the housing using an elastic adhesive agent.
If an elastic adhesive agent (such as a rubber adhesive agent, urethane adhesive agent, silicone adhesive agent, elastic epoxy adhesive agent or the like) is used, the platform may be elastically held by the housing using a simple construction, which enables easy manufacture and assembly of the apparatus.
According to another aspect of the invention, the platform is held by the housing via a spring member.
Based on this construction, if an appropriate material and shape are selected for the spring member, a prescribed spring coefficient may be obtained with ease and accuracy. Therefore, it is easy to ensure that the platform is elastically held by the housing in the desired condition.
According to another aspect of the invention, the platform has an essentially cylindrical configuration, and is aligned such that the central axis thereof matches the longitudinal central axis of the electromechanical conversion element along which it extends and contracts.
Based on this construction, because the platform is made symmetrical relative to an axis, oscillation in an unnecessary oscillation mode, i.e., in the directions perpendicular to the directions in which the electromechanical conversion element extends and contracts, for example, may be prevented to the extent possible. Therefore, fluctuations in the driving characteristic may be further prevented. In addition, because the platform has a configuration that is symmetrical relative to the central axis thereof, and is aligned such that this axis matches the axis of the electromechanical conversion element, it becomes no longer necessary to adjust the angle of the platform to the electromechanical conversion element, making assembly of the apparatus easy.
Furthermore, according to another aspect of the invention, the platform has an outer circumferential surface in which protrusions and indentations are formed.
Based on this construction, the surface area of the outer circumference of the platform is increased due to these protrusions and indentations. Consequently, the amount of heat released from the platform increases. Therefore, the heat generated by the electromechanical conversion element may be efficiently released from the platform, enabling an increase in the temperature of the electromechanical conversion element to be prevented.
In addition, according to another aspect of the invention, the electromechanical conversion element has an essentially cylindrical configuration.
Based on this construction, because the electromechanical conversion element has a configuration that is symmetrical relative to an axis, oscillation in an unnecessary oscillation mode, i.e., in the directions perpendicular to the central axis of the electromechanical conversion element along which it extends and contracts, for example, may be prevented to the extent possible. Therefore, fluctuations in the driving characteristic may be further prevented. In addition, where the electromechanical conversion element is aligned such that the axis thereof matches the axes of the driving member and platform, it becomes no longer necessary to adjust the angle of the electromechanical conversion element to the driving member and platform, making assembly of the apparatus easy.
Moreover, according to another aspect of the invention, the driving member comprises a rod member having a circular cross-section, and is aligned such that the central axis thereof matches the longitudinal central axis of the electromechanical conversion element along which it extends and contracts.
Based on this construction, because the driving member has a symmetrical configuration relative to an axis, oscillation in an unnecessary oscillation mode, i.e., in the directions perpendicular to the directions in which the electromechanical conversion element extends and contracts, for example, may be prevented to the extent possible. Therefore, fluctuations in the driving characteristic can be further prevented. In addition, because the driving member has a configuration that is symmetrical relative to a central axis thereof and is aligned such that this axis matches the axis of the electromechanical conversion element, it becomes no longer necessary to adjust the angle of the driving member to the electromechanical conversion element, making assembly of the apparatus easy.
Furthermore, according to another aspect of the invention, the electromechanical conversion element is directly elastically held by the housing.
Based on this construction, the platform may be eliminated, which makes the construction and assembly of the apparatus simple.